1. Field of the Invention
The present invention relates to an automatic focusing camera one particularly, having a photographic lens with variable focal length.
2. Description of the Prior Art
Until now, the so-called active type automatic focusing camera has been designed so that photographic lens focusing is adjusted by projecting the light beam from the light emitting elements toward the object and detecting the light beam reflected from the object by the light sensing element. However, in the conventional automatic focusing camera, the range in which the distance is measured (hereinafter called the focus target) is limited to a remarkably narrow range in the middle of the photographic picture plane so that the object to be photographed is not well focused unless the object to be photographed is located in a predetermined position in the middle of the photographic picture plane. Generally, the object to be photographed should be located within the distance measuring mark provided in the view finder.
Consequently, quite recently, an automatic focusing camera has been proposed, in which a plurality of focus targets are set in the photographic picture plane to obtain a well focused picture regardless of the position of the object in the photographic picture plane. FIG. 1 shows an example of the distance measuring system of such an automatic focusing camera. In the drawing, a light emitting element array 1 has a plurality of light emitting elements 1a-1e, a light projecting lens 2 projects the light beams produced by the light emitting elements 1a-1e towards respective focus targets 6a-6e provided in the horizontal direction of the photographic picture plane, and a light sensing element 3 whose signal output changes based on the incident position of the light beam, for example, a PSD (position sensitive device). A light receiving lens 4 serves to lead the projected light beam reflected from the object in the respective focus targets 6a-6e to the light sensing element 3. In this example, the projected light beams of the respective light emitting elements 1a-1e are reflected by the objects existing along the respective direction of the focus targets 6a-6e and the respective reflected light beams are sensed by the light sensing element 3 at the light sensing positions according to object distances based upon the principles of trigonometry. The output of the light sensing element 3 changes based on the light sensing position so that information regarding the distance to the focus target 6a-6e from the illuminant light emitting element 1a-1e can be obtained from the output. By obtaining the distance information for the respective targets 6a-6e a well focused picture can always be obtained regardless of the position of the object in the photographic plane.
When the focal length of the photographic lens of such an automatic focusing camera is variable, the following problems occur. The so-called variable focus camera having a photographic lens with variable focal length is disclosed in Japanese Laid-Open Patent Application No. Sho 57-141084.
In the variable focus camera, the photographic picture angle changes based on the change over of the focal length of the photographic lens so that there is a possibility that the object distance of the photographic picture plane is also measured if the above automatic focusing camera is provided with a plurality of focus targets. Namely, as is shown in FIG. 1, the photographic picture angle .beta. at the side of the long focal length of the photographic lens is smaller than that .alpha. at the side of the short focal length, so that when a plurality of focus targets 6a-6e are provided corresponding to the photographic range 5a at the side of the short focal length, the object distance outside the photographic range 5a, namely the object in the focus targets 6a and 6e are also measured. In such a case there is a danger that the result of the distance measurement would be wrong due to unnecessary distance information, while the light emitting elements 1a and 1e are also wastefully lit.
It is, accordingly, an object of the present invention to provide an automatic focusing camera capable of measuring a wide range of distances by setting a plurality of focus targets in the photographic picture plane, so designed that when the photographic picture angle changes due to the changing of the focal length of the photographic lens the distance is measured by the focus targets provided in a number corresponding to the pnotographic picture angle, in order to avoid mismeasurement of the distance.
Further objects and features of the present invention will become apparent from the following description of the preferred embodiment with reference to the accompanying drawings.